Succulent plants, or succulents, are plants that store water in their enlarged fleshy leaves, stems, or roots. The enlargement is usually due to the greater amount of the parenchyma tissue.
heuffelii, type from Romania, in cultivation, a member of the Crassulaceae, storing water in its thick leaves. Photo: Manuel Werner, Germany
Although all plants store water, succulent plants are especially adapted to store water for longer periods. This allows them to survive in arid environments, where they receive little competition from other plants and less herbivory. During the day, their habitat is rather hot. However, when the habitat is cool at night, the succulents can respire. In the morning, often dewfall helps the plants to survive. Some succulents try to take up as much moisture from the dew as possible by having large surface area by long hair.
Many succulents have a waxy coating on their stems and leaves, helping them to retain moisture. Having a large internal volume for storage but minimum surface area is also important to prevent drying up. CAM photosynthesis is also a common feature found in many succulents for water conservation.
Succulence is a feature due to convergent evolution and is not necessarily an indication of genetic relationship. There are succulents in many unrelated families (more or less 50, some sources note only 28). However, for some families, most members are succulent; for example the Cactaceae, Agavaceae, Aizoaceae, and Crassulaceae.
The table below shows the number of succulent species found in some families:
- http://www.sukkulenten.ch (in German)
- http://www.lapshin.org/succulent/ (English/Russian)